Old, large cold air return vents are consuming our AC too fast. HELP!

7 years ago

last modified: 7 years ago

Can I place filters over my cold air return vents on the floor? I rent a house that was built in 1923. It is only 900 square feet, and has a basement where the AC system is located. Our main floor is all one level. We have three cold air return vents on the floor. Two are in the living room/dining room which is one big open room. One is in the hallway under the thermostat. All of the return vents on the floor are huge, measuring 1.5 feet by 2.5 feet. The grills on them have large, numerous holes, measuring 1 inch by 2 inches. Our air conditioning will run for an hour just to reduce the house temperature by 2 degrees. (For the record, our regular vents that *blow* the air are also on the floor. Everything is on the floor........)

If I have to reduce the house temperature from 80 degrees down to, say, 75 degrees, the AC will run nonstop for up to 4 hours. I've noticed that the suction on these cold air return vents is very strong. It sucks debris down into the vents very easily. I am wondering if these vents are just so large that they are sucking the AC back down before it can just barely reach the thermostat positioned high up on the hallway's wall. I placed some filters over each of these vents. There are air holes in them, but it is slowing down the suction. It took 11 minutes for the house temp to lower 2 degrees. The house retained its target temperature for 10 minutes, then kicked the AC back on. It ran for another 11 minutes, then turned off. Is this ok? Prior to attempting these filters, the system kept running and running. It did this so badly that it ran out of freon and the coil froze. Someone had to come service it and replace the freon. I've noticed the system isn't running itself into the ground when I place filters over these large return vents. Let me know if this poses a problem. I realize covering return air vents is not advisable, but this is more of a filter, to slow down the system from over-consuming our air before it even has a chance to reach the thermostat.

p.s. Our filter is brand new. Our thermostat is brand new with new batteries. Freon has been put back in the system as of one week ago. The ducts might be leaky, I don't know. This house is old as crap and I am willing to bet the ductwork is too. We don't own, however. We rent, so we can't do much about the ducts if they have holes. Unless anyone has suggestions...

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Comments (3)

ionized_gw
7 years ago
I can't recommend restricting the return air flow. Have you found the main system filter? That should take care of your needs. 4 hours to reduce the temp 5 degrees is not, in itself, an indication of a problem. Was that at a very hot time? Neither is cycling on and off for a 50% cycle. Running continuously on a hot day is not an indication of a problem either.

Please consider posting some pictures of the nameplate on your indoor and outdoor units.

I am afraid that if you can't get the landlord to fix the system, your best option might me to get some window units. That way, at least at night, you could cut your electric consumption by cooling only the bedroom with a relatively efficient unit. Be sure that your electricity is up to the task before you buy.
Vith
7 years ago
last modified: 7 years ago
Prior to attempting these filters, the system kept running and running. It did this so badly that it ran out of freon and the coil froze.

Has nothing to do with the return size and location. Your supply ductwork is insufficient, unable to get enough CFM to get the cold off the coil before it freezes.Also makes sense why it has to run so much to cool the house, there isn't enough supply airflow.

Btw, your AC system does not "run out of Freon" from being overused, the Freon is recirculated and goes through an evaporating and condensing phase which transfers heat. Systems lose Freon through leaks that can develop over time.
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I personally would really like to help you but it would be way too difficult and time consuming without a lot of up front technical information. Most of us like to "do it right" from the ground up. I think you'll find that fooling with this and that will take up a lot of time to maybe some but,no real efficient end. I understand your need to pull the purse strings. But if your duct work is sweating, that is certainly part of your problem. Is this flexible duct inside a fiberglass insulation sleeve or when you say flexible duct, is it various sizes of dryer vent? If so, you may have to start replacing it anyhow if the insulation got wet, as money allows. I would suggest doing so with rigid insulated ducting. Join the duct run of the month club and by the end of next year you might be finished. This is obviously an add-on unit before you got there. There is no way for us to determine if it was sized properly for the home and if the coils are matched properly. It almost sounds like a mobile home unit adapted to your house. The guy before you might have been saving money too and cheated on the sizing. Your blower unit speeds will also need to be known. I think your best bet would be to go to the book store, library, on line and educate yourself on air distribution. For example, the size of a room will determine if that room should have one or two supply registers and/or returns and what size they should be. You'll need to know the pro's and con's of mounting the supply's or returns high or low. Although the learning will not necessarily be that hard, it is a must have. Just the little information I mentioned here is a drop in the bucket for all the things that must be known and considered. Either you learn or pay someone who has already learned or you can use a lot of coat hanger wire and duct tape and hope for the best. Go ahead and shove the return up through the opening if you can, that's better than doing nothing to try to make things better. If you have that much play, you are losing a lot of air flow due to resistance and excessive length. You shouldn't have any sags at all. Even metal ductwork not properly installed can cost you in proper distribution. For example, a 90 degree elbow placed in the wrong place and not properly installed, can cause you to lose 50-60 percent of air flow, due to blockages and resistance caused by a vortex of the air within that bend. Just too much to really effectively cover here, at least in my opinion.
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Since you now have the name of the original installer, have him come back and look things over, and ask him about those holes. He probably knows more about that unit than anyone else. One more thing, please do not mess around waiting. It seems you are already living in that house, and you have no idea, why those holes are there, or what could be in the air you are breathing. This could cause a serious health hazard. Get the original installer in there, and get whatever it is taken care of fast.l
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Air and Energy Soutions
7 years ago
It sounds like your home had floor furnaces at one point. The large return air grilles sound like old openings for floor furnaces, used a long time ago. Where to start?

First, your system should have filters somewhere in the return duct or inside the air handler or furnace. I would look really good to make sure you haven't missed something. I've seen filters placed in really weird places. Sometimes filters aren't found for years. By then they're pretty stopped up. As far as the return grilles being large, the larger the better! One thing that kills your system and your energy efficiency is duct work that's just too small. Modern systems are made to run with very little static pressure in the ducts, around 1/2 inch. That's not much, so I wouldn't worry about the large ducts. The filters are another story. You really need a filter in your return duct somewhere. If there's not one, i would install filtration. Usually the cheapy filters work best as they cause the smallest pressure drop in the duct.

You mentioned the refrigerant leaking out. If you have a refrigerant leak it should be repaired. That stuff ain't cheap. Besides it's illegal for a technician to keep adding without repairing the leak. If someone is having to add refrigerant, you definitely have a leak, no question about it. If the service provider you called did not look at your duct work, did not tell you your system had a leak, and did not offer sound recommendations, please ditch them and find someone qualified.

As far as your system coming on and off every ten minutes or so, that's called "short cycling" and isn't good for your system, your energy costs, or your comfort. It sounds almost like your system is either too large for your home or you have massive air infiltration. Either way, this needs to be addressed. Really, I would recommend you find a good service provider in your area that can be trusted to offer technically correct advice. I usually find it best to ask friends, co-workers, or other family who they use and trust. In the meantime, you may want to check out a couple of articles I've written dealing with heat loads and your comfort. Here's one HERE if you would like to read it.

Let me know if there are specific things I can help with. I'll be happy to help if possible.

Old, large cold air return vents are consuming our AC too fast. HELP!

Comments (3)

ionized_gw

Vith

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